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Video: Estimating the Measure of an Angle

Tim Burnham

Which of the choices is closest to the measure of angle 𝐵𝐴𝐶? [A] 126° [B] 48° [C] 228°.

01:34

Video Transcript

Which of the choices is closest to the size of angle ๐ต๐ด๐ถ?

Now to identify which angle weโ€™re talking about, ๐ต๐ด๐ถ tells us about the journey that we have to make, so we go from ๐ต to ๐ด to ๐ถ. And then the angle weโ€™re talking about is this enclosed angle here.

Now remember three hundred and sixty degrees is a full turn like that. If we do half a turn, we get a hundred and eighty degrees. And if we do quarter of a turn, we get ninety degrees. And no turn at all is zero degrees.

Angles in between zero and ninety are acute, angles in between ninety and a hundred and eighty degrees are obtuse, and angles between a hundred and eighty and three hundred and sixty are reflex.

Now the angle weโ€™ve been given here is obtuse; itโ€™s bigger than ninety degrees but itโ€™s not quite as big as a hundred and eighty degrees.

Now the fact that itโ€™s bigger than ninety degrees means it canโ€™t be angle โ€œ๐ตโ€. The fact that itโ€™s not as big as a hundred and eighty degrees means it canโ€™t be โ€œ๐ถโ€, which leaves us with โ€œ๐ดโ€, and that looks like about a hundred and twenty-six degrees. So our answer is โ€œ๐ดโ€, one hundred and twenty-six degrees.